First-level interconnect (FLI) structures may include bulk solder interconnect structures to couple a die with another component (e.g., another die or substrate) of an integrated circuit (IC) package assembly. As dies continue to shrink to smaller dimensions, a pitch between individual structures of the FLI structures may also shrink and present various process and/or reliability risks for bulk solder interconnect structures. For example, in a thermocompression (TCB) bonding technique, defects associated with solder bridging may occur where solder on adjacent pillars/pads fuses together during reflow. Smaller pitch between FLI structures may further result in undesirable solder wicking that may lead to voids due to contraction and/or reaction of inter-metallic compound formed during reflow. These defects may exacerbate stresses on inter-layer dielectric (ILD) or other stress junctions (e.g., passivation layer) resulting in delamination and/or cracks that compromise the reliability of the IC package assembly. Such defects may presently be mitigated by increasing control of solder volume and/or bonding/retract force requirements, however such control may be approaching limits of current technologies.
Further, through-mold interconnects (TMIs) are emerging in package-on-package (PoP) IC package assemblies to reduce an overall height of the package assembly (e.g., for mobile devices). A height of solder in the TMIs may be dependent on various factors including height of the molding compound, die thickness and package warpage effects. It may be desirable to control height and/or collapse of solder and reduce defects associated with solder bridging or ball merging in such PoP assemblies.